Slurry pump with screened discharge for preventing lump accumulation



Nov. 25, 1952 2,619,292

L. A. NICHOLS, JR, ET AL SLURRY PUMP WITH SCREENED DISCHARGE FOR TING LUMP ACCUMULATION ed Nov. 29, 1949 A TTORNE'Y Patented Nov. 25, 1952 UNITED STATES PATENT OFFICE SLURRY PUMP WITH SCREENED DIS- CHARGE FOR PREVENTING LUMP AC- CUMULATION poration of Delaware Application November 29, 1949, Serial No. 129,906

1 Claim. 1

This invention relates to an improved pump and circulating system for hastening the preparation of viscose from cellulose xanthate, aqueous caustic soda, and water.

In the normal preparation of cellulose xanthate many particles agglomerate into lumps or balls and these relatively large agglomerates resist dissolving and generally have to be broken up into many smaller pieces before a satisfactory solution can be made therefrom. Because of this difliculty in dissolving lumps of cellulose xanthate,

a number of difierent type mixers have been especially designed for dissolving cellulose xanthate in aqueous caustic solutions. These have at least one feature in common in that the xanthate lumps are forced between rigid members moving relative to each other to tear or squeeze apart the lumps of cellulose xanthate. The mixers are so designed that the clearance between moving and stationary parts is relatively small and by pumping actions and circulation within the mixer, particles are repeatedly mashed or squeezed through these relatively tight passages. In spite of the skillful design and workmanship that has gone into these mixers, the time consumed in satisfactorily mixing a batch of viscose is commonly of the order of four hours. Attempts to decrease this time have always been accompanied by poor filterability and high fiber count in the viscose. Accompanying this, poorer spinning and yarn of inferior physical properties ultimately result. In addition, the cost in time and power is very substantial. Accordingly, a long wished for desideratum has been to reduce this time substantially without sacrificing filterability.

It is an object of this invention to provide a pump which obviates the above difiiculties. It is a further object to provide a pump which permits substantial reduction in time and power without a loss in the filterability of the final vis cose. Other objects appear hereinafter.

These objects are accomplished by inserting a perforated plate on the discharge or outlet side of a standard pump such as a Viking pump, as illustrated in Figure l. The screen is situated so that it is in comminuting relationship with certain moving parts of the pump, namely, the impeller. The objects are thus accomplished by converting a normal pump functioning chiefly as a pump to a pump which functions not only as a pump but as an attrition mill. The modified pump is used in a circulating line connected to the mixer, blender, homogenizer, constant index viscose system, or the like.

By pumping and circulating the partially mixed xanthate and aqueous caustic soda solution through the modified pump of this invention the viscose mixing time is reduced as much as 25-35% or more. Even with this very substantial reduction in mixing time, the filterability is substantially the same. If desired, filterability can be greatly improved by maintaining the mixing time the same as before. This invention is not only applicable to preparing the initial solution of the cellulose xanthate or premixing but may also be used to advantage in connection with final mixing, blending, and may also be used in connection with viscose circulating systems,

as for example a constant index viscose system described in U. S. Patent 2,087,016 (Bradshaw and McKee).

This invention will be more clearly understood by reference to the following discussion and to the figures, given for illustrative purpose only, of which Figure 1 is a longitudinal cross-section of the pump of this invention;

Figure 2 is a perspective of the perforated plate of this invention and Figure 3 is an end view of the perforated plate.

Referring to the figures, the pump contains a supply inlet 2 through which is passed a slurry containing large lumps of cellulose xanthate 3. These are highly swollen and if unremoved they cause poor filterability in the final viscose. Inside the pump is an impeller or rotor 4 and an idler gear 5 moving counterclockwise about a fixed pivot 6. Spacer 1 is provided to assist in the pumping. At the discharge end 8 a perforated plate or screen 9 is inserted. The large lumps of xanthate are forced through the small holes of this plate and are considerably reduced in size. The teeth of the idler gear and the rotor or impeller push the lumps through the perforations and the rotor moving close to the plate prevents lump accumulation. The particles become the size of the perforations Or smaller. These small particles Ill are then passed on to the mixer, dissolver, disintegrator or whatever unit is the next receiver in the particular line assembly being used. The idler gear and spacer need not be present; it is only necessary that the pump have an impeller which will pump the slurry from the intake to the discharge port and force the slurry through the perforated plate.

In one test using a Viking pump equipped with the screen with A1 clearance between the screen and the pump rotor, the following results were obtained on filterability. For a control the same general set-up was used but the perforated plate was omitted from the pump. With the normal mixing cycle of 3 hours and 50 minutes the filterability of this normal viscose in the control is arbitrarily set as 100%. Examples taken from a number of runs and averaged together show that after 2 hours of mixing with this modified pump set-up the filterability was equal to 98%, at the end of 3 hours was equal to 104%, and at 3 hours and 50 minutes was equal to 105%. The substantial saving in time and in power without any substantial change in quality of the end products is highly advantageous. This is especially true in the regenerated cellulose field in which more economic operations are essential.

The perforated plate of this invention may be constructed of any material capable of withstanding the pressure and also the alkaline conditions prevailing in the pump. Usually it is made of steel. It is generally curved, as shown to fit the pump and contains a plurality of holes ll about inch in diameter. The particular plate used in the above experiments had about 300 such holes. The pump that is modified by the means of this invention may be any rotary pump providing there is positive pump displacement, passages suificiently large to accommodate the lump material to be handled and room enough so that suflicient clearance between the perforated plate and pump rotor, may be maintained to prevent lump accumulation on the discharge side. This clearance is usually about inch and is essential to prevent excessive pump pressures from being developed.

It is, of course, possible to vary the plate size and shape, hole size and number, etc. A plurality of plates may be employed of the same or different hole size.

Besides affording the advantages of decreased operation time and costs, the apparatus of this invention permits operation under more uniform pressure. For example, when the modified pump of this invention is used in the viscose ripening line, the usual viscose skins or gels that occur and cause pressure fluctuations are eliminated. The smaller particles readily pass through the relief side of the pressure regulating valves. More uniform pressure of the viscose being supplied to the spinning machines results with attendant improved spinning.

Any departure from the above description 4 which conforms to the present invention is intended to be included within the scope of the claim.

We claim:

In a rotary positive displacement pump of the gear-within-a-gear type having a liquid impeller gear rotating with close clearances within a surrounding casing which closely conforms to the circumference of the path traced by the impeller and an inner, eccentrically located idler gear meshing with the impeller during a portion of said path to provide a positive displacement of liquid from an inlet port in said casing, the improvement which comprises forming said discharge port of a perforated plate conforming to the internal shape of said casing with a clearance of about A; of an inch from said impeller and provided with a plurality of openings of about 21 2' of an inch in diameter.

LOUIS ALBERT NICHOLS, J R. LLOYD VVESCOTT.

REFERENCES CITED The following references are of record in the file of this patent:

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